With the increasing popularity of playing streaming audio and video over networks such as the Internet, there is a need for optimizing the data transferred from a server to a client such that the client's experience is maximized even if network conditions during playback are inconsistent. Optimizing the client's experience involves making encoding decisions such that the video can be transferred and reconstructed with a minimal number of errors.
The term “streaming” is typically used to indicate that the data representing the media is provided by a host computer over a network to a playback device (i.e., a media playback computer implemented as any of a variety of conventional computing devices, such as a desktop PC, a notebook or portable computer a cellular telephone or other wireless communication device, a personal digital assistant (PDA), a gaming console, etc.) The client computer typically renders the streaming content as it is received from the host, rather than waiting for the entire file to be delivered.
The quality level is generally dictated by the bit rate specified for the encoded audio or video portions of the input stream. A higher bit rate generally indicates that a larger amount of information about the original audio or video is encoded and retained, and therefore a more accurate reproduction of the original input audio or video can be presented during video playback. Conversely, a lower bit rate indicates that less information about the original input audio or video is encoded and retained, and thus a less accurate reproduction of the original audio or video will be presented during video playback.
Generally, the bit rate is specified for encoding each of the audio and video based on several factors. The first factor is the network condition between the server and the client. A network connection that can transfer a high amount of data indicates that a higher bit rate can be specified for the input video that is subsequently transferred over the network connection. The second factor is the desired start-up latency. Start-up latency is the delay that a video playback tool experiences when first starting up due to the large amount of data that has to be received, processed, and buffered. Start-up latency can also occur after a seek operation, where the user selects variable positions in the streaming content to view. A third factor is the processing capabilities of the playback device. The fourth factor is the tolerance to glitching. Glitching occurs when the content is not displayed at the rate it was authored causing the playback device to run out of data to display. In most cases any amount of start-up latency or glitching is intolerable, and it is therefore desirable to optimize the bit rate specified such that the start-up latency and the glitching are minimized or eliminated.